Which type of fire stream pattern would be least effective in combating a structure fire?

A full fog stream pattern is least effective in combating a structure fire because it disperses water over a wide area, creating a fine mist that may not provide adequate cooling or reach the hot gases and flames effectively. While fog patterns can be useful for specific applications, such as thermal protection or reducing heat exposure in certain situations, they do not deliver the concentrated energy needed to penetrate and suppress the heat and flames present in a structure fire.

In contrast, straight streams and solid streams are designed to deliver water directly and efficiently to the seat of the fire, maximizing the impact on the fire and enhancing cooling. A power cone provides a focused conical spray that combines the benefits of both straight and fog streams, allowing for effective heat absorption and fire suppression while maintaining penetration capabilities. The increasing effectiveness of these more targeted stream patterns highlights why a full fog stream is typically not the best choice for combating a structure fire.